The proposed research program aims to begin to test whether anxiety is categorical or dimensional in nature. In years 1 and 2 of the research program, a series of investigations will empirically evaluate the structural nature of three anxiety disorders: generalized anxiety disorder, posttraumatic stress disorder, and social phobia. Each disorder will he examined in large clinical and analogue samples using sophisticated taxometric procedures designed to test latent structures. Follow-up analyses will inspect the overlap between the three disorders to increase understanding of their frequent comorbidity. In years 3 and 4, a therapy outcome investigation will assess the efficacy of a classification scheme (either categorical or dimensional) derived from taxometric analysis of generalized anxiety disorder. The investigation will compare this classification scheme to traditional DSM-IV diagnosis on the relative ability to predict prognosis, treatment response, and functional outcome following a brief clinical intervention for chronic worry. Results of the proposed research are expected to enhance scientific understanding of the nature of anxiety, with important implications for the conceptualization, assessment, investigation, and treatment of the anxiety disorders.